Jump to content

and now for something completely different part 3


kevin gilmore
 Share

Recommended Posts

Report from cuisine de joamat.

One side of the balanced board works alright – able to set output current and offset is within a millivolt. The other side – output current controllable but servo doesn’t work as desired, offset, varies round plus two and a half volt.

Here is an aerial picture of the output board.1745502272_BZ8A0332(2).thumb.jpg.f5ca396ccf917bd39bf1d364fa6cbaf3.jpg

I’m not so happy to dive in with test pins in there… and servo parts on the bottom side. :mikey2:

…maybe I should be satisfied with one working side out of two possible. :dance:

  • Like 2
Link to comment
Share on other sites

  • 1 month later...
On 2/13/2018 at 7:49 PM, jose said:

My amp module is ready. Now I'm working on a second Psu for the amp (dual-mono) and at the same time I work on the unbal/bal preamp (I have the PSU ready). I want to do a three module system.

a71294a59322889d13a8cfd5eceed88a.jpg

Hey Jose, very nice amp. Mind asking which cases are you using here? Is the sink estate enough to cool all the transistors for CFA3 balanced with 4 channels? 

 

Can someone please point me to the latest gerbers for the CFA3 balanced amp - looks like here in this post is the latest revision? Appreciated, thanks!

As for the PSU the GRLV is it, right. Some building it with 24 or 30 volts? 

Here in this post BOMs for the CFA2 and GRLV 30V.

Edited by starcat
Link to comment
Share on other sites

I usually use Modu boxes. They are expensive (I live outside the continent) but they do the job.

That heatsink is overkill for a single CFA. Even for 2 CFA's they are still a bit oversized (BIAS 190mA).

24vDC power supply. Use OPA445.

  • Like 1
Link to comment
Share on other sites

I suspect using here the 1/2w Xicon 273 50PPM resistors shouldn't be a problem instead of the 1/4w Vishay 100PPM from the BOM? I have a couple of the Xicon's laying around... 

Edited by starcat
Link to comment
Share on other sites

6 hours ago, jose said:

I usually use Modu boxes. They are expensive (I live outside the continent) but they do the job.

Very nice indeed. I can however find the Modu Slim line only with profile sides but not with sinks. Do you have a link or model number for the one on the right (with the sinks and milled aluminium front)? 

Edited by starcat
Link to comment
Share on other sites

1 hour ago, jose said:

I don't want to be rude or impertinent but please, use your browser and spend some time looking for the information.

As you can see I have spent more than some time and even posted the link above. It is simply that I do not find a 1U enclosure with sinks on the sides. Might be that it is discontinued or whatever. If you don't want just don't bother answering. Doesn't mean I have not researched the whole site already. 

1 hour ago, Pars said:

Is the one on the right a 2U? Looks to be 1U from the pic.

The SlimLine have 10mm sides which would be sufficient for heatsinking for many applications.

Exactly, the left is the SlimLine with the profile sides and 10mm milled front as in the shop. The right however looks identical in hight but with sinks and a sinked version isn't available in the shop. Might be that he had it modified though with the sinks. Doesn't really look to me like being 2U. 

Edited by starcat
Link to comment
Share on other sites

Thanks. Although the GRLV is very clean and stable, for preamps I prefer to use R-cores and easier to place in a single chassis since they do not electromagnetically interfere (or very little) with anything. It´s optional so you can perfectly use a toroid

Now that I've seen the preview, it's been a little over a year since Dr. Gilmore sent me a design for a new buffer based on the CFA architecture. At the moment I have not been able to put it into operation. If confinement and anti-virus measures allow it this year I could have it ready.

Edited by jose
orthography
Link to comment
Share on other sites

The key difference between a toroid and an R-core is primary/secondary capacitance and leakage inductance.

R-core has primary and secondary on opposite legs. So the capacitance is low, but the leakage inductance is high.

With a toroid, the capacitance is high, but the leakage inductance is low.

So an R-core (like a split bobbin EI) is better for not coupling RFI between windings. But the leakage inductance means enough stray magnetic field to cause potential hum problems.

A toroid by contrast, because of the tight coupling between the windings, tends to couple RF. But because of the low leakage inductance has a very low external magnetic field.

Basically, horses for courses. I've used both types in various bits of my kit. But since I always use an outboard supply (for non-power amp use) either type has worked just fine.

  • Like 3
Link to comment
Share on other sites

Does anyone have a pair of CFP3 boards they want to get rid of?

Also, I see two sets of Gerbers: cfp3rs and cfp3rss. Is the difference the revised servo/current mirror? I'm assuming the cfp3rss is the most recent?

Thanks!

Link to comment
Share on other sites

6 hours ago, Pars said:

Does anyone have a pair of CFP3 boards they want to get rid of?

Also, I see two sets of Gerbers: cfp3rs and cfp3rss. Is the difference the revised servo/current mirror? I'm assuming the cfp3rss is the most recent?

Thanks!

Hi @Pars

 

I think I have some spare boards with the latest version, that has the servo completely out of the audio path, as Kevin said. Tomorrow I let you know. 

Best 

Tiago 

Edited by ti5002000
Edit
  • Like 1
Link to comment
Share on other sites

Unclear. Going back in the thread, I had posted this, as the schematics I have don't appear to have this fix in place. Shortly after this post, you released new gerbers including all fixes. However, there was an error with a 10K resistor connecting to a device emitter instead of the base. Not sure whether the fixes mentioned were in only referring to this or also included the servo fix. I don't see a pair of 15K resistors, as were used in the CFA2 fix, on the gerbers.

 

Link to comment
Share on other sites

11 hours ago, Pars said:

Unclear. Going back in the thread, I had posted this, as the schematics I have don't appear to have this fix in place. Shortly after this post, you released new gerbers including all fixes. However, there was an error with a 10K resistor connecting to a device emitter instead of the base. Not sure whether the fixes mentioned were in only referring to this or also included the servo fix. I don't see a pair of 15K resistors, as were used in the CFA2 fix, on the gerbers.

 

Sorry @Pars i wasn´t thinking right..What i have is the CFA2...

My mistake..

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...